Apparatus for augmenting mass and velocity of exhaust streams



Sept. 14, 1954 P PITT APPARATUS FOR AUGMENTING MASS AND VELOCITY OFEXHAUST STREAMS Flled Nov 13, 1945 INVENTOR. PAUL A. PITT ATTORNEYPatented Sept. 14, 1954 APPARATUS FOR AUGMENTIN G MASS AND VELOCITY OFEXHAUST STREAMS Paul A. Pitt, San Diego, Calif., assignor to SolarAircraft Company, San Diego, Calif., a corporation of CaliforniaApplication November 13, 1945, Serial No. 628,108

8 Claims.

This invention relates to the treatment and disposal of exhaust gasesfrom combustion devices generally, and has particular application to theinternal combustion engines of aircraft.

An object of the invention is to increase the reaction force of theexhaust stream from a combustion device.

Another object is to increase the mass and temperature of the gas streamdischarged from the exhaust pipe of a combustion device.

Another object is to complete combustion of unburned components of theexhaust gas of a combustion device.

Other more specific objects and features of the invention will appearfrom the description to follow of certain specific embodiments of theinvention.

It is well known that the stream of gas issuing from the exhaust pipe ofan internal combustion engine has a thrust effect, which, if the exhaustpipe is directed rearwardly, in the case of aircraft, helps to propelthe craft. In the case of a jet engine, the entire propulsive force isproduced in this way. In the case of an ordinary engine, most of thethrust is obtained from the propeller which is rotated by the engine,and the thrust resulting from the reaction of the gas stream issuingfrom the exhaust pipe is relatively small. The reaction force dependsupon the volume of the gas being discharged, which in turn depends inpart upon the temperature. In the case of an aircraft having a propellerdriven by an internal combustion engine, a substantial portion of theheat of combustion is abstracted in the engine, with a correspondingreduction in the temperature and pressure of the exhaust gas. However,the exhaust gas usually contains unburned constituents representingenergy that is wasted.

In accordance with the present invention, the temperature and volume ofthe gas discharged from the exhaust pipe is substantially increased bysecondary combustion within the exhaust duct, with the addition ofoutside air. The addition of the outside air not only supplies oxygenfor the complete combustion of unburned fuel components appearing in thegas discharged from the engine, but adds to the total volume of gasdischarged. It is not broadly new to attempt to produce secondarycombustion in the exhaust pipe by the addition of air thereto, but tothe best of my knowledge previous attempts to produce secondarycombustion in this way have been unsuccessful, for all practicalpurposes, because of the difflculty of initiating and maintaining the(Cl. Gil-35.6)

secondary combustion. This difficulty is overcome in accordance with theinvention by introducing into the exhaust pipe, in addition to auxiliaryair, additional fuel which facilitates the ignition and burning of theunburned constituents of the exhaust gas.

I find it desirable to introduce the auxiliary air and mix it with theexhaust gas before the resultant mixture is mixed with the fuel. It isalso desirable to introduce the fuel in the form of a combustibleair-fuel mixture which may be supplied under pressure from thesupercharger of the engine. The stream of fuel and air from thesupercharger is preferably ignited by a spark plug, hot wire, or otherigniting device prior to its mixture with the exhaust gas, as thispromotes thorough combustion of all unburned components in the exhaustgas.

A full understanding of the invention may be had. from the followingdetailed description of certain specific embodiments thereof asillustrated in the drawing, in which Fig. 1 is a side elevation view ofan aircraft en ine assembly to which the invention is applied, theconventional parts of the assembly being shown in broken lines and theadded structures in accordance with the present invention being shown infull lines;

Fig. 2 is a 1ongitudina1 section on a larger scale of the structureshown in full lines in Fig. 1, the plane of the section being indicatedby the line 11-11 of Fig. 3;

Fig. 3 is a front end view of the structure shown in Fig. 2; I

Fig. 4 is a detail horizontal section taken in the plane IVIV of Fig. 2;

Fig. 5 is a longitudinal section showing a design alternativeto that ofFig. 2, the plane of the section being indicated by the line V-V of Fig.6; and.

Fig. 6 is a cross-section taken in the plane VI VI of Fig. 5.

Referring first to Fig. 1, there isshown in broken lines the mainelements of an aircraft engine unit. These elements include a nacelle IDin which the engine is mounted, an engine II to which is attached apropeller I2, an enginedriven supercharger 13 through which fuel-airmixture is supplied to the engine, and an exhaust manifold M throughwhich exhaust gas from the engine is discharged.

The intake of the supercharger I3 is shown connected to a carburetor [5,which, as shown, receives air from a scoop IS the inlet end of whichextends exterior of the nacelle l0 and faces forwardly so that the slipstream past the nacelle it, when the airplane is in flight, builds upair pressure in the scoop l6.

Ordinarily, the exhaust manifold [4 would be directly connected to theatmosphere through a tail pipe H, which, in this instance, is showndischarging through the' tail end of the nacelle H]. In accordance withthe present invention, however, a special structure is interposedbetween the exhaust manifold M and the tail pipe I! for producingsecondary combustion of the exhaust gas and increasing its heat contentor enthalpy.

Referring now to Figs. 2 and 3, the special structure for producing thesecondary combustion comprises a tubular coupling element 23 which isconnected at its forward end 2| to the exhaust manifold l4 (Fig. 1) andis connected at its rear end 22 to the forward end of the tail pipe IT.This coupling member may be formed in three parts for convenience inmanufacture and assembly, and as shown, it consists of a front section23, an intermediate section 34, and a rear section 24. The two sections34 and 24 are secured together by a clamp 25. The intermediate section34 telescopes into the rear end of the front section 23 and may bewelded thereto.

Exhaust gas entering the forward end 2| of the section 23 from theexhaust manifold M is directed through an inner tubular member 26,

which tapers to a smaller diameter at its rearward end and is traversednear its rear end by a hollow mixing duct 21, the opposite ends of whichextend through the wall of the member 26 and are open. As best shown inFig. 4, the member 21 is of airfoil shape and is provided with dischargeapertures 28 in its rear inwardly tapering side walls.

Air is supplied into the annular space between the tubular members 23and 26, respectively, through an intake duct 29 the forward end of whichis positioned at the leading edge of the nacelle l0 (Fig. l) and therear end of which opens through the wall of the member 23. The airentering the annular space 30 flows rear wardly through a second innertubular deflector member 3| which, like the inner tubular member 26,- istapered inwardly and rearwardly, the space substantially enclosed bydeflector 3| in which the air supplied through the intake 29 is mixedwith the combustion products supplied through the member 26 may betermed a mixing zone. The front large end 32 of the member 3| is ofsomewhat smaller diameter than the intermediate outer section 34, andthe annular space between the two members is filled by a channelshapedmember 33 which defines with the section 34 an annular space 35 for apurpose to be described later. The front half of the channelshapedmember 33 is imperforate and forces all of the air entering the annularspace 33 to flow into the front end 32 of the inner tubular member 3|.Due to the constriction of the rear end of the member 3| and thecross-sectional shape of the member 21, some of the air entering themember 3| flows into the opposite ends of the cross member 2! and isdischarged through the apertures 28 therein into the exhaust streamflowing through the member 26. The remaining air is mixed with theexhaust gas and air issuing from the outlet end of the member 26 and theresultant mixture is discharged at substantial velocity through themember 3| into the rear casing section 24 where it is mixed with fueland ignited. The portion of the casing 24 rearwardly of the deflector 3|together with the forward portion of the tail pipe I! thus forms a maincombustion zone.

The structure for supplying the fuel includes the annular channel member33 which, together with the mid casing section 34, defines the annularpassage 35. Thus, the rear portion of the front casing section 23 isprovided. with an annular corrugation 31 near its rear end, which, withthe mid casing section 34, defines an annular space 38, and this space38 is supplied with a mixture of fuel and air through a pipe 39 (Fig. 1)leading from the supercharger l3 of the engine.

That portion of the mid section 34 of the casing that is interposedbetween the annular spaces 35 and 38, respectively, is perforated atintervals as indicated at 40 to permit passage of the fuel-air mixturefrom the annular passage 38 to the an.- nular passage 35, and it isdischarged from the annular space 35 through circumferentially spacedholes 4| in the rear wall of the channel member 33.

The fuel-air mixture leaving the apertures 4| enters an ignition chamberor sheltered combustion zone including the annular space 42 between theinner tubular member 3| and the outer member 24, where it is ignited byany suitable means, such as a spark plug 43 to form a continuouslyburning primary or ignition flame as long as fuel is supplied via pipe39. The burning mixture flows rearwardly around the inner taperedtubular member 3| and mixes with the mixture of exhaust gas and airdischarged through the member 3|.

The annular channel member 33 is exposed on its front and inner sides tothe cool air that flows through the annular space 30. This is desirablebecause it cools the combustible fuel-air mixture in the channel 35,thereby preventing starting of combustion within the channel.

Because of the velocity of the air and exhaust gas mixture turbulence iscreated in the mixture as it leaves the tapered tubular member 3 i. Itis, accordingly, thoroughly mixed with the burning air-fuel mixtureleaving the ignition chamber 42, so that substantially all of the fuelcomponents in the exhaust are completely burned and their energy used toraise the temperature of the exhaust gas and air.

As a result of the additional air introduced into the exhaust systemthrough the duct 29 and the volume increase resulting from the increasedtemperature produced by the combustion, the volume and velocity of thegases issuing from the tail pipe I! are greatly increased so that amaterial thrust effect urging the aircraft forwardly is obtained.

Flow of air through the air intake duct 29 is produced in part bypressure developed at the forward end of the duct (resulting either fromthe motion of the airplane or the thrust of the propeller |2) and inpart by the suction resulting from the flow of exhaust gases through andout of the inner tubular member 26. Thus, as a result of the streamlinedcross-sectional shape of the cross member 21, the flow of exhaust gastherepast produces a reduced pressure adjacent the apertures 28 thattends to draw air therethrough. Likewise, the relatively high velocityof the exhaust gases issuing from the reduced rear end of the tubularmember 26, reduces their pressure at that point, which tends to draw airinto the member 3| from the annular space 30.

The tail pipe I! should be of relatively large diameter and only longenough to allow the gases to burn completely. However, a compromise mustsometimes be resorted to because of the size and shape of the nacelle.If the tail pipe is longer than necessary it results in additionalfrictional loss, whereas if it is too short the burning may not becompleted within the pipe, and flame will be discharged. In either eventthe thrust obtained will be somewhat reduced.

The structure described has been very successful in practice, operatingsmoothly and positively, despite the fact that it is usually verydifficult to initiate and maintain smooth combustion in a high velocitygas stream. Tests indicate that the chief reason for the success of thestructure is that only the marginal portion of the stream leaving themember. 3| is mixed sufficiently to support combustion, and the flameresulting from the burning of this marginal portion ignites remainingportions of the stream progressively as they become sufficiently mixedto burn. Because of the fact that there is no instantaneous ignition ofa large body of combustible mixture, explosions and rough burning andpopping are prevented. The burning of the gas stream leaving the member3| commences at the downstream edge of member 3|, but extends downstreamas it moves into the center of the stream. The gas passing through themember 3! is moving at much higher velocity than the gas in the ignitionchamber 42, and this produces swirling and eddy currents which promotescombustion at the edge of member 3|.

It has been found in tests made on apparatus of the dimensions stated,that by the introduction of only 600,000 B. t. u. per hour from the fueltaken from the supercharger, the heat of the exhaust gas is boosted from6,000,000 to approximately 18,000,000 B. t. u. per hour. In other words,the heat of the fuel added to the exhaust pipe by my apparatus sets freeabout twenty times as much heat from unburned constituents in theexhaust gas that would otherwise be wasted.

In the modified structure of Figs. 5 and 6, the positions of the exhaustgas and air passages are reversed. Thus, in Fig. 5, the air entersthrough an inner tubular member 50, the forward end 5| of which is openso that air is rammed into it by the forward motion of the airplane. Therear end of the member 50 extends into the inturned end 52 of a middletubular member 53, the latter being bulged outwardly exterior of itsinturned end 52, to form a manifold space 54 which may be directlyconnected by a short coupling conduit 55 directly to the exhaustmanifold M of the engine (Fig. 1).

The exhaust gas flowing through the annular passage 54 flows rearwardlythrough an annular passage 56 defined between the inturned end 52 andthe juxtaposed side wall portion of the mid section 53 and is mixed withthe air entering through the front section 59. The mid section 53 istapered to a reduced diameter at its rear end and projects into the.enlarged forward end 5'! of the rear section 58 which may connect to thetail pipe I I (Fig. 1) or may discharge directly into the atmosphere.

The forward end 51 of the rear section 58 is connected to the midsection 53 by an annular channel-shaped member 59 which is welded to theexterior surface of the section 53. The forward end of the rear section51 may in turn be welded to the outer wall of the channel member 59. Thechannel member 59 functions together with the wall of the mid section 53to define an annular manifold 60 which receives combustible mixture fromthe pipe 39 and discharges it through openings 62 in the rear wall ofthe channel member 59 into the rear tubular section 58 where it isignited by a spark plug 64 and thereafter mixed with the mixture ofexhaust gas and air issuing from the rear end of the mid section 53.

Although for the purpose of explaining the invention two specificembodiments thereof have been disclosed in detail, various departuresfrom the exact structure shown will be apparent to those skilled in theart, and the invention is limited only to the extent set forth in theappended claims.

I claim:

1. An afterburner comprising an outer duct having a first inlet adaptedto be connected to an engine exhaust pipe; a mixing duct within saidouter duct and connected to said outer duct to receive all of theexhaust gases entering said first inlet to mix them and direct themaxially of said outer duct; a transversely disposed element within saidmixing duct for mixing and more evenly distributing the flow of gasestherethrough; an annular chamber between said first and second ducts; anair intake connected to said annular chamber; a tubular member withinsaid outer duct and disposed in alignment with said mixing duct toreceive the exhaust gases therefrom and the air from said annularchamber, said tubular member forming a protected annular primarycombustion zone surrounding the mixture of gases and air within saidmember; a wall between said tubular member and said outer duct at theupstream end of said member to prevent the passage of gases into saidprimary combustion zone; a distributor for supplying fuel evenly Y tosaid annular primary combustion zone; and

an igniter for initiating combustion in said primary combustion zone toestablish a continuously burning primary flame in a zone surrounding andcommunicating with the blast of mixed exhaust gases and air issuing fromsaid tubular member and which ignites matured and burnable portions ofthe mixture in a peripheral zone downstream of said tubular member withresult that the remainder of the mixture burns downstream of saidtubular member.

2. Propulsive thrust generating apparatus comprising a duct structurallyformed to present netforward propulsive reacting surfaces; a mixing zonein said duct through which gases containing combustion components pass;means for supplying a component to form a combustible mixture with saidgases in said mixing zone; a main combustion zone in said ductdownstream of said mixing zone; means for causing said combustiblemixture to flow through said main combustion zone at a velocity higherthan the normal rate of flame propagation through said mixture; anannular structure forming a sheltered combustion zone adjacent said mainmixing zone and causing turbulent flow of gases from said maincombustion zone into said sheltered zone; ignition means for saidsheltered zone; and means to deliver combustible fuel mixture to saidsheltered zone operative to maintain anchored igniting and combustionsupporting flame which mixes with said turbulent flow of gases topropagate flame across said combustible mixture in said combustion zonecausing the generation of a thrust producing gaseous mass reactingagainst said surfaces.

3. For use in combination with the exhaust outlet of an internalcombustion engine; propulsive thrust generating apparatus operative inany position comprising 9. mixing Z0116 through which gases containingcombustion components pass and a main combustion zone downstream of saidmixing zone, structurally formed to present forward propulsive thrustreacting surfaces; means for supplying a component to form a combustiblemixture with said gases in said mix ing zone; a mixture deflector alonga substantial portion of the periphery of said mixing zone forming botha sheltered combustion zone and a turbulent ignition zone adjacent theupstream end of said main combustion zone; ignition means for saidsheltered zone; and means to deliver combustible fuel mixture to saidsheltered zone operative to maintain anchored igniting and combustionsupporting flame which mixes with and ignites said mixture in saidturbulent zone and causes continuous flame propagation across mixture insaid main combustion zone with said mixture traveling at a velocityhigher than the rate of normal flame propagation in the mixture and withthe generation of a thrust producing gaseous mass reacting against saidsurfaces.

4. Propulsive thrust generating apparatus having forwardpropulsivethrust reacting surfaces comprising: a duct; means forintroducing into said duct a plurality of fluids which, When mixed, forma combustible mixture; means including a deflector forming a mixing zonein which said fluids are formed into said combustible mixture, saiddeflector extending along at least a substantial portion of a peripheryof said mixing zone and forming a Wall of a sheltered combustion zone,and creating turbulence downstream of said sheltered combustion zone;means forming a main combustion zone downstream of said mixing zone; andmeans eifective to establish and maintain an ignition flame in saidsheltered combustion zone which ignites said combustible mixture in saidmain combustion zone and causes continuous flame propagation across saidcombustible mixture in said main combustion zone with zone with saidmixture travelling at a velocity higher than the rate of normal flamepropagation in the mixture to cause thrust producing acceleration ofsaid gases reacting against said surfaces.

5. The combination defined in claim 4 wherein said deflectorperipherally bounds said sheltered combustion zone.

6'. The combination defined in claim 4 wherein said deflectorperipherally bounds said sheltered combustion zone and said mixingzone.-

7. The combination defined in claim 4 wherein said deflector hassurfaces inclined with respect to the axis of said duct which interceptand deflect said fluid away from said sheltered combustion zone.

8. The combination defined in claim 4 wherein said deflector hassurfaces inclined with respect to the axis of said duct whereby thesectional area of said sheltered combustion zone increases in adownstream direction.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 791,002 Busey May 30, 1905 1,315,931 Poppink Sept. 9, 19191,824,820 Hynes Sept. 29, 1931 1,830,658 Hynes Nov. 3, 1931 1,839,880Hyatt Jan. 5, 1932 1,938,851 McKee Dec. 12, 1933 2,047,471 Hepburn et alJuly 14, 1936 2,184,967 Winter Dec. 26, 1939 2,304,008 Muller Dec. 1,1942 2,395,919 Sundell Mar. 5, 1946 FOREIGN PATENTS Number Country Date309,273 Italy July 1, 1933

